1. Field of the Invention
The present invention relates to a process for preparing copper phthalocyanine blue pigments characterized by good dispersing properties.
2. Prior Art
The introduction of phthalocyanine pigments in 1935 set new standards of excellence in the pigment consuming industries. They are characterized by their excellent light fastness, intensity, bleed and chemical resistance, extreme stability, and exceptionally high tinting strength. Phthalocyanine pigments are restricted to the blue and green regions of the spectrum. Because of their excellent color values, working properties and low cost in addition to durability, phthalocyanine blue and green pigments are used extensively.
It is desirable in the production of phthalocyanine blue to develop a product which will attain approximately 90 percent of its maximum strength by dispersing the dry powder in the vehicle using a high speed agitator. To accomplish this goal, it is necessary to find some means of protecting the particles when the aqueous cake is dried, thus reducing sintering and the formation of aggregates. This can be achieved by extending the product while in the aqueous phase with a suitable resin. Further, resinated pigments are generally softer in texture and disperse more readily in oil-ink applications, when compared to unresinated pigment. However, phthalocyanines must undergo some form of particle size reduction either by acid pasting or salt grinding. Resinating a phthalocyanine is complicated by the presence of strong acid and/or large amounts of salt, making it necessary to filter and wash out the excess salt or acid and reslurry the aqueous cake for resination which adds a great deal to the manufacturing cost of any product. Accordingly, it is a purpose of the instant invention to avoid the need for reslurrying.